Journal of Stress Physiology & Biochemistry, Vol. 3 No. 1,
2007, pp. 4-17.
Original Text Copyright (cc) 2007 by Hajiboland, Hasani
ORIGINAL
ARTICLE
Data source : Google Scholar
QueryDate : 2016-12-24
Cites : 8
EFFECT OF Cu AND Mn
TOXICITY ON
CHLOROPHYLL FLUORESCENCE AND GAS EXCHANGE IN RICE AND SUNFLOWER UNDER
DIFFERENT LIGHT INTENSITIES
Hajiboland* R., Hasani B.D.
Plant Science
Department, University
of Tabriz 51666 Tabriz, Iran Fax: +98 411 3356027 e-mail: ehsan@tabrizu.ac.ir
Received January 12, 2007
Abstract - Copper (Cu) and
manganese (Mn) are essential micronutrients
for plants, but toxic at high concentrations. Responses of rice (Oryza
sativa L.) and sunflower (Helianthus annuus L.) to toxic concentrations
of Mn and Cu (up to 100 μM) were studied under three light intensities
including low (LL, PPFD=100), intermediate (IL, PPFD=500) and high (HL,
PPFD=800) light intensities in hydroponic medium. Rice plants showed
higher susceptibility than sunflower to both heavy metals concerning
dry matter of shoot and root. Growing under higher light intensity
strengthened the effect of Cu toxicity while ameliorated that of Mn,
the latter was attributed to the lower Mn accumulation of HL plants in
both shoot and root. Chlorophyll content of leaves was influenced
negatively only by Cu treatment and that at the highest concentration
in the medium (100 μM). Similar with growth results, reduction of net
assimilation rate (A) was higher in HL than LL plants treated by excess
Cu, but in contrast to growth response, reduction was more prominent in
sunflower than rice. Excess Mn-induced reduction of A was similar
between LL and HL plants and was greater in sunflower than rice.
Reduction of A was partly attributable to stomatal limitation, but
non-stomatal mechanisms were also involved in this reduction. Copper
and Mn treatment did not change the optimal quantum efficiency of PSII
in dark-adapted chloroplasts (Fv/Fm ratio), but Fv/F0 was influenced
particularly by Cu treatment, the reduction was higher in rice than
sunflower and in HL compared to LL plants. Regarding excess Cu and
Mn-mediated alterations in chlorophyll concentration, Fv/F0 and Tm
values, it was suggested that, Cu and Mn toxicity depress the leaf
photosynthetic capacity primarily by causing a significant alteration
of the composition and functional competence of the photosynthetic
units rather a reduction in the number of photosynthetic units (PSUs)
per unit leaf area.
Key
words:
Cu toxicity, Chlorophyll fluorescence, Gas exchange, light intensity,
Mn toxicity
